Corrosion resistant and cold workable molybdenum steel



UNITED STATES PATENT OFFICE CORROSION RESISTANT AND COLD WORK- ABLE MOLYBDENUM STEEL Heinrich Reitz, Bitterfeld, and Erich Hengler and Alfred Biittinghaus, Wetzlar, Germany No Drawing. Application March 10, 1938, Se-

rial No. 195,104.. In Germany May '7, 1935 1 Claim.

The present application relates to steels capable of resisting attack by corrosive media including aqueous solutions of chlorine, hypochlorous acid and their salts and is a continuation-in-part of our co-pending application Serial No. 78,316 filed May 7, 1936.

One of the chief problems with which the present day metallurgists are faced is a meeting of the demand by the chemical arts for steels which will Withstand corrosive chemicals and still be capable of being mechanically worked. This problem is particularly onerous as regards those industries which employ solutions of chlorinecontaining substances, since, as is known, ferrous metals are very susceptible to attack. by these substances. In fact, screens and the like used in filtering apparatus in the manufacture of hypochlorites, when made of so-called stainless steel, are so vigorously attacked that their utility is completely impaired after only short periods of service.

Chromium is one of the alloying elements which is most commonly employed in steels designed for use in chemical apparatus. This element has the 2 function, among others, of improving the corrosion resistance of the steel. Molybdenum has recently come into rather extended use, usually with chromium as an agent for increasing or imparting corrosion resistance. Neither this element not chromium, nor both together, however, is capable of giving steels this property to an extent suflicient to withstand the attack of different chemicals especially solutions of chlorinecontaining substances. Moreover, molybdenum, 35 when used in large amounts, has a marked tendency to render steels brittle thereby impairing their capability of being mechanically worked in the cold, that is cold rolled, cold drawn and cold hammered. Any increase in corrosion resistance resulting from the use of large proportions of molybdenum is, therefore, offset by a decrease in the mechanical cold workability of the steels.

The purpose of this invention is to provide a chromium-molybdenum low-carbon steel which 45 will be resistant to attack by aqueous solutions of chlorine, hypochlorous acid, their salts and the like, and at the same time will possess the desired mechanical properties of being cold rolled, cold drawn, cold hammered and the like to a high no de ree.

We have discovered that if there is included in low carbon-chromium-molybdenum steels an alloying ingredient capable of forming carbides, in such quantities that after a fixing of the free carbon as carbide there remains suflicient of the ingredient to form mixed crystals with the other alloying ingredients, steels of a resistance to chlorine-containing solutions which could not be foreseen are obtained. The alloying ingredient that we have found most suitable for use and which We therefore prefer, is titanium. Preferably the titanium is present in an amount from about 6 to 12 times the amount of the carbon present. However, other elements may be used in lieu of titanium with satisfactory results. Thus, 15 such carbide-forming elements as vanadium, tantalum, uranium, niobium, cerium, boron, zirconium and tungsten may be used as substitutes for titanium. It is of course to be understood that when such other carbide-forming elements are used to replace the titanium, they will be used in amounts equivalent to the amount of titanium employed. In this connection cognizance should be taken of the fact that titanium carbide has the formula TiC; vanadium carbide the formula VC; tantalum carbide the formula TaC; uranium carbide the formula U203; niobium carbide the formula NbC; cerium carbide the formula CeCz; boron carbide the formula BeC; zirconium carbide the formula ZlCz and tungsten carbide the formula W2C. It will be seen from a simple computation based on these formulae and the molecular weights of the elements in question that for each part of titanium there should be used about 1.1 parts of vanadium; about 3.8 parts of tantalum; about 7.5 parts of uranium; about 1.9 parts of niobium; about 1.45 parts of cerium; about 1.4 parts of boron; about 1 part of zirconium and about 7.6 parts of tungsten.

As previously noted, we have found it preferao ble in making up our alloys to maintain a low content of carbon, that is less than about .5%. The chromium content of the alloys should range between about 12 and 30%, preferably between about 20 and 30%. The molybdenum content may be as high as 5% and should exceed about 1.5%. The titanium should be present in an amount of from about .5 to 3.5%. The same is true if vanadium or zirconium is used in place of titanium. On the other hand, if boron or cerium be so used, they will be present in an amount of from about .7 to about 5% The amount of tantalum which would be employed in lieu of titanium would be about 1.9 to about 13.3%. The quantity of uranium or tungsten which would be present as a substitute for the amount of titanium would be from about 3.8 to about '26.3%. Niobium, if used, would be present in an amount of from about .9 to about 6.7%. The addition of small amounts of manganese and silicon are also to be recommended. Thus the steel preferably contains from about .3 to about .6% of manganese and less than .5% of silicon. The addition of copper in an amount not exceeding 3% has the efiect of further increasing the corrosion resistance of the steel. The balance of the steel is iron with the usual negligible quantities of impurities generally present in stainless steels.

These steels, especially when prepared with titanium, not only are remarkably resistant to corrosion by chlorine-containing solutions but also possess the property of being cold rolled, cold hammered and cold drawn. An estimate of their resistance to corrosion may be gleaned from the fact that said steels are capable of withstanding attack by the very corrosive calcium hypochlorite solutions even at a temperature of C. Said steels may, therefore, be employed for all purposes where steels of these properties are required. Thus they are admirably fitted for the manufacture of wire screens for filtering chlorineand hypochlorite-containing mashes and lyes 91nd perforated supporting discs for such filters as well as armatures, armature accessories, pumps, containers, valves, slide bars and the like which during use contact chlorine-containing solutions.

The following illustrates typical alloys within the scope of our invention:

Per cent (1) Carbon =less than 0.50

Manganese 0.30- 0.60 Silicon less than 0.50 Chromium 12.5 -30.0 Molybdenum 1.50- 5.00 Titanium Vanadium .5 3.5 or Zirconium Uranium or Tungsten or Niobium .9 6.7

or Cerium or Boron Balance iron and negligible quantities of usual impurities.

Per cent (2) Carbon less than 0.10

Manganese 0.40- 0.60 Silicon =less than 0.50 Chromium 16.0 -18.0 Molybdenum 1.80- 2.40 Titanium 0.80- 1.20 Balance iron and negligible quantities of usual impurities.

Per cent (3) Carbon 0.20- 0.30 Manganese 0.40- 0.60 Silicon =less than 0.50 Chromium 23.0 -25.0 Molybdenum 2.80- 3.30 Titanium 1.80- 2.40 Balance iron and negligible quantities of usual impurities. L

Per cent (4) Carbon 0.18- 0.22

Manganese 0.40- 0.60 Silicon less than 0.50

Chromium 27.0 -29.0

Molybdenum 1.60- 2.00

Titanium 1.20- 1.60

Balance iron and negligible quantities of usual impurities.

Balance iron and negligible quantities of usual impurities.

Per cent (6) Carbon less than .1

Manganese .4 .6 Silicon less than .5 Chromium 16 -18 -Molybdenum 1.8 2.4 Tantalum 3v 4.6 or Niobium 1.5 2.3

Balance iron and negligible quantities of usual impurities.

Per cent (7) Carbon .2 .3 Manganese .4 .6 Silicon less than .5 Chromium 23 -25 Molybdenum 2.8 3.3 Cerium 2.6 35

or Zirconium 1.8 2.4

Balance iron and negligible quantities of usual impurities.

Per cent (8) Carbon .18- .22

Manganese .4 .6 Silicon less than .5' Chromium 27 -29 Molybdenum 1.6 2 Uranium 9 or Tungsten Balance iron and negligible quantities of I usual impurities.

Titanium has heretofore been used in steels but primarily for the purpose of effecting de-oxidation thereof. This use is inno way comparable to our use of titanium. On the contrary, the presence of titanium in our steels serves the purposes of augmenting the corrosion resistance of the steel imparted by the molybdenum and of preventing the molybdenum from destroying the desired mechanical properties of the steel such as its cold rollability, cold ductility and cold malleability. Thus, the steels have a much greater resistance to corrosion than could be imparted to them by molybdenum alone, and at the same time are capable of being mechanically worked in the cold despite the presence of substantial quantities of molybdenum.

The twofold function of the titanium in our steels is developed in the accompanying tables which compare the corrosion resistance and cold malleability of chromium-molybdenum steels with chromium-molybdenum-titanium steels.

less than about .5% of silicon, from about 12 to about 30% of chromium, from about 1.5 to about 5% of molybdenum and a carbide-forming element of the 4th to 6th group of the Periodic System selected from the class consisting of The asterisks in the above tables indicate that the results were not ascertained with particularity since it was apparent from observation that the test pieces had sufiered a very material decrease in weight, a fact which was to be expected at the outset.

For a full discussion of the Erichsen test referred to in the tables attention is directed to page 154 of Enzyklopaedie der technischen Chemie by Ullmann, volume 4, 2nd edition.

It is to be understood that similar results will be obtained when there is used, in place of titanium, the carbide forming elements mentioned above.

What we claim is: a

Cold ductile and cold malleable corrosion-resisting alloys for use in the manufacture of articles which require resistance to attack by aqueous solutions of chlorine, calcium hypochlorite and their salts, containing less than .5% of carbon, from about .3 to about .6% of manganese,

Loss of weight in grams/sq. meter of surface in 1 hour Depth in 0 Mn s1 Cr Mo Ti 20 H.so.+ mm. in a figg 'g g- 4% mm. foil 1 mm. perature a 5%? 2.225% 90 Erichsen Loss of weight in grams/sq. meter of surface in 1 hour NaO Cl-soluo M s1 0 M Tl i g 33 Deptb in n r o gms. mm. in a of chlorine foil 1 mm. t 0 6 at 0 0 4158110. 811df in 1101211985 grams 0 ace. 0

C110], at Erlchsen 0. 27 0. 40-0. 60 0. 30-1 24. 83 2. 0 10. 5 0. 027 Strong pitting. 6.5. 0. 07 0. 40-0. 60 0. 30-1 26. 70 2. 30 10. 0 ----d0 7.1. 0. 20 0. 40-0. 60 0. 30-1 26. 28 1. 88 1. 39 0. 00 0. 0058 N0 attack--- 7.5. 0.08 0.40-0.60 0. 30-1 29. 15 1. 71 1. 29 0. 00 0. 0000 do 8.2- 0. 27 0. 40-0. 60 0. 30-1 26. 28 4. 00 4. 5 Pitting Not kcifiii of from about 3.8 to about 6.3% while always exceeding by about 45 to 90 times the amount of carbon, the niobium being present in an amount of from about-.9 to about 6.7% while always exceeding by about 12 to 24 times the amount of carbon, and the cerium being present in an amount of about .7 to about 5% while always exceeding by about 9 to 18 times the amount of carbon, the balance being iron with the usual impurities.

HEINRICH REITZ. ERICH HEN GI..E R. ALFRED B'U'I'I'INGHAUS. 

